A fuel cell generates electric power using a fuel gas, and because the fuel cell is able to generate thermal energy used as hot water supply heat at the same time when it generates electric power, enhancement of energy efficiency can be achieved.
A conventional load controlling device for a fuel cell increases efficiency of the fuel cell by controlling devices that consume electric power and hot water supply heat supplied by the fuel cell (for example, see Patent Document 1). For example, in a case where an amount of electric power generation by the fuel cell is different from an amount of main power electricity, which is an amount of electric power for an entire house, devices consuming electric power are controlled to run or stop, so that an amount of main electric power and an amount of electric power generation are maintained at the same amount. In addition, because the fuel cell generates thermal energy when it generates electric power, it becomes unable to generate electric power unless the generated heat is removed. To this end, the fuel cell is provided with a hot water storage tank to use thermal energy for a supply of hot water. In a case where an amount of hot water storage in the hot water storage tank exceeds the maximum capacity, devices consuming hot water supply heat are controlled to run for consuming thermal energy.
FIG. 21 is a block diagram showing the configuration of a conventional load controlling device described in Patent Document 1. Referring to FIG. 21, a load controlling device 203 acquires an amount of main electric power, which is an amount of electric power consumption by an entire house, an amount of electric power generation by a fuel cell main body 201, and an amount of hot water storage in the hot water storage tank from the fuel cell main body 201, and acquires an operating time, an amount of electric power consumption, and an amount of hot water usage from devices 202.
An electric power demand predicting portion 204 predicts an electric power demand, and outputs a predicted amount of electric power to a consumption control portion 206 together with the amount of main electric power acquired from the fuel cell main body 201. In a case where the amount of main electric power is different from the amount of electric power generation, the consumption control portion 206 outputs a control signal to the devices 202 so that they are run to make the amount of main electric power equal to the amount of electric power generation. Also, a hot water supply demand predicting portion 205 predicts a hot water supply demand, and outputs the predicted amount of hot water supply to a heat control portion 207 together with the amount of hot water storage acquired from the fuel cell main body 201. In a case where the amount of hot water storage exceeds the tank capacity, the heat control portion 207 outputs a control signal to the devices 202 so that they are run to reduce the amount of hot water storage for enabling the fuel cell 201 to operate continuously.
In the prior art described above, however, in a case where a control method of devices consuming electric power is determined, it is determined on the basis of the amount of main electric power and the amount of electric power generation alone, and no consideration is given to thermal energy that is newly generated when the control method is changed. By merely controlling devices so as to make the amount of main electric power equal to the amount of electric power generation, there may be a case where thermal energy is generated in an amount exceeding an amount of thermal energy used by the user. In addition, in a case where converted thermal energy is so large that it exceeds the tank capacity, thermal energy has to be released or when thermal energy cannot be released, the fuel cell has to be stopped until the tank becomes available owing to hot water supply load, which possibly compromises energy saving.
Another problem of the prior art described above is raised by the configuration in which devices are classified into devices consuming electric power and devices consuming hot water supply heat and the devices consuming electric power are controlled according to the amount of main electric power while the devices consuming hot water supply heat are controlled according to the amount of hot water storage. Household electric appliance, however, includes devices consuming both hot water supply heat and electric power. In a case where such a device is controlled, even when a device consuming both hot water and electric power is started immediately before hot water reaches the full tank capacity in avoiding such an event, thermal energy generated from the fuel cell increases because the fuel cell generates electric power in response to an increase of the amount of main electric power. Hence, there may be a case where it is impossible to avoid an event that an amount of hot water storage reaches the full capacity. In other words, because an amount of hot water supply heat consumption and an amount of electric power consumption by the devices are taken into account separately in the conventional load controlling device, there may be a possibility that the load controlling device fails to enhance energy saving.
Patent Document 1: JP-A-2001-68126